Automatic switching telephone system



'June 6, 1944. A. J. BUSCH ETAL AUTOMATIC SWITCHING TELEPHONE SYSTEM I Filed Dec. 26, 1942 8 Sheets-Sheet 1 .I.I.I..I.L

A. J. BUSCH VI. RE um W H HsM W. S

m M N B w A 7' TORNEV 8 Shets-Sheet 2 A.J. BUSCH LHJIENRV 8y 0. F. SE/BEL' A T TORNEV v IN 5 IV 7095 Filed Dec. 26, 1942 A. J. BUSCH ETAL AUTOMATIC SWITCHING TELEPHONE SYSTEM w l .i L

June 6, 1944.

June 6, 1944. A. J. BuscH EI AL ,8

AUTOMATIC SWITCHING TELEPHONE SYSTEM Filed Dec. 26, 1942 8 Sheets-Shee t 5 FRAME .9

I T I I FRAME .5

'1 .4 .J. BUSCl-I //VVNTORS I. H. HENRY;

c. F. SE/BEL WmHV A 7' TORNE V Jim 6, '1944.

A. J. BUSCH -ETAL AUTOMATIC SWITCHING TELEPHONE SY STEM Filed Dec. 26, 1942 8 Sheets-Sheet 4 .4../. euscH INVEN 7 019s /.'H.HERY By c. SE/BEL ATTORNEY June 1944, A. J. BuscH EI'AL 2,350,873

AUTOMATICSWITCHING TELEf'HONE SYSTEM Filed Dec. 26, 1942 8 Sheets-Sheet 5 .4../. auscw v INVENTOR$= mus/m c. r. SEIB'E'L AUTOMATIC SWITCHING TELEPHONE SYSTEM Filed Dec. 26, 1942 8 Sheets-Sheet 6 v A J. BUSCH mvavrms: H. HENRY CJ-I SEIBEL er wwh g A T TORNEV June 6, 1944. A. J. BuscH ETAL AUTOMATIC SWITCHING TELEPHONE SYSTEM Filed Dec. 26, 1942 8 Sheets-Sheet 7 V r W MRF N w? M BH w W JHHF W A A C W. R M m K N 5 w \\m W 3 Juhe 6, 1944.

A. J. BUSCH ETA].

AUTOMATIC SWITCHING TELEPHONE SYSTEM Filed Deg. 26, 1942 8 Sheets-Sheet 8 QNM MRM mun. i W i b A r mn M 0. m T Y W. B

A T TORNE Y Patented June 6, 1944 'Ij-JToMATro SWITCHING TELEPHONE 1 sYsTEM Aloysius J.-Busch,-Maglison, Israel H. Henry, East.- oranga andcliarles F. Seibel, Glen Rock, N. J.,, assignoi's to Bell'l Telephone Laboratories, Incorporated; New York; N. Y., a corporation of eassessment26, 1942, Serial No. mazes 1 1 Claims. (01. 179-2 7) This; invention relates to automatic switching telephone systems and more particularly to mean locations of switches connected to individual trunks. According to: the present invention a miilti-freouency' signaling system: is providedghavingnuplh cate-multi'frequency current supply setsarran'ged forralt'ernate" connection with the switches of an automatic switching system by a controlamechanism for progressively transmitting signals of I different combinations of currents of. differentifre.

quencies: to a plurality of. tuned receiving circuits in markers, for effecting the operation of switch locating devices in said markers-:todirectthez operation of the markers? for locatiiig and operating switchesconnected with selected incomingand outgoing 'trunks' and: "intermediate jqinnctor switches for completing telephone connections.

A feature of the invention. resides in .an: automatically operable controlled mechanism for periodically connecting alternate duplicate multi- 'frequency signaling current? supply setsto .the mechanism of an automatic switching system, with automatically operable means provided to nullify the periodic transfer when a failure occurs in the multifrequenc'y syster'nfa'nd place th'e'ialternate signaling current supply set inu's with the mechanism of the switching. system. a I

Another and related feature of the invention resides ina fault analyzing circuit associatedwith the automatically. operable control mechanism and. the switching system,. combined with: ail-signaling current supply'set transfer mechanism and so arranged thata Visible signal istenergizedlto erence may be had to the accompanying drawings,

in which:

Fig. 1 illustrates duplicate iniiltifreciiiency rentsupplysets; I f V .7

Fig. 2 the frame equipm'entrfor the multii re quency' current sets and the switching system;

Fig; 4 illustrates. diagrammatically a marker with a plurality of receiving circuits therein associated with the multifrequencycurrent supply sets and switch locatingdevices; i g Figs. 3, 5, 6; 7 and' 8 illustrate controLmechanism for controlling the association of alternate multifrequency current sup-ply: sets; with the switching system in which Figs; 7 and, 8 illustrate switches for controlling-the. periodic; transfer; of the multifrequen'cy current supplyjsets; and- Figs/3,5 and 6 illustrate devicesfor nullifyin-g the periodic transfer mechanism and causing an arbitrary transfer from one. multif-requency current supply set having a fault therein to the-a1ter--. nate multifrequency current supply set.;-- j The system chosen to illustrate features of this invention is in general similar to the one disclosed in Patent 2,236,246 to GLV; King et-a1., March 25, 1941. In the presentsystein' automatic switches of the crossbar type are disclosed; for selectively establishing the: desired; connections 'a'nd these switches arecon'trolled by common reg;- ister" senders and commdnfinarkers: Theic-ross bar switches, the senders and markerslfor-controlling said switches, the marker connectors for connecting the markers to said senders and-the frame connectors which serve to associatethe markers with the cross bar switch frames-and 'the methods whereby the switchesare controlled 2,021,329 of November 19;:1935;

General description; I

The multifrequency signaling system shownlin .Patent 2,236,246 issued March 25, 1941;.to G.

King; J B. McKim, and O. Myers is in general of the same character asthe muitirreque ys'ys- V item shown herein along with the contro cnit :and control mechanism of the: invention e system disclosed in the patent, however; depends upon one-current source supply setof a vplurality :Of'frequencies instead of duplicate currentsource supply sets such as I00 and H0 herein} ,ShOWn which are controlled in a mannertg prevent th possibility; of incomplete telephone: -connetions because offailures in any part of -the multifre :quency signaling system. The telephone switch- .ing systemmay be of the same character as shown that an incoming call energizes an incoming trunk F H circuit for the actuation of a link system which associates the incoming line with a sender in which registrations are recorded as transmitted over the line from a distant subscriber or a distant telephone oflice. The code registration recorded by the sender is transferred to a. marker for the selection of one outgoing trunk and the operation of the switches. Let it be assumed, for example, that a registration has been made for connecting an incoming trunk from a distant offlce to an outgoing trunk extending to another distant oflice. The code registration for the selection'of this outgoing trunk is set up in the marker by theisender which has been selected for this purpose. A route relay in themarker is thus actuated which will bring about the selection of an idle outgoing'trunk extending to this particular ofiice by associating the marker with a group of -terminals.with' which these outgoing trunks are associated. To accomplish this a connector is energized for associating the marker with particular trunk block relays which may be connected to the group or groups of outgoing trunks extending to an o-fiice-for' which the call has been registered. When an idleioutgoing trunk to this particular office is available, information is transmitted by'signals to the-marker which makes successive operations for completing the connection. I

Any character of incoming trunk from various types of offices or subscribers may be connected to any character of outgoing trunk in this automatic switching telephone ofiice. In view of the many characteristics of the different trunks and in view of the number of groups and subgroups into which these trunks must necessarily be divided, considerableinformation must be trans- :j

mitted to the: marker from various sources to guide the marker in-completing a connection from an incoming trunk of a particular character, connected to a cross bar switch mounted on one of a large plurality of incoming trunk switch frames, to an outgoing trunk of the same or different character connected to a cross bar switch mounted on an outgoin trunk switch frame. f I

; Due to the complexities of a mechanical switching system and the flexibilities required, no permanent connection is made between the marker and the cross bar switches. Frame connector units are used for connecting a large number of incoming secondarycross bar switches and out- I going primary cross-bar switcheswith the-marker for establishing icircuit paths over leads between anincoming primary cross bar switch to which a, callingjincomlng trunk is connected and an outgoingsecondary; cross barswitch to which an I idle outgoing'trunk is connected. -These frame connector units are, however, selected by the marker through the aforementioned connectors according to the location of' the -incoming trunk and, outgoing trunk switches'overfcertain frames after the location of these switches i indicated by a multifrequency signaling circuit to the "switch isfassociate'd' with the marker through the marke rfi The-lncoming trunk primary cross-bar trunks. latter group, a multifrequency signal is automatically transmitted to the marker giving the assignment connector which, with the exception of the incoming trunk bear no designated or numerical relation to the incoming primar switch or the frame on which this cross bar switch is mounted. These units of equipment may be used for calls from many diffrentincoming trunks connected to variouslylocated incoming primary switches. This is also true of the outgoing trunk 10- secondary cross bar switch which is associated with the--marker through the outgoin trunk equipment, patching jacks which are used for fiexibilities in arrangin trunk groups, trunk group relays and connectors.

7 equipment which are common to different frames of switches, the multifrequency signaling system is, included in this mechanical switching system to transmit signals to the marker giving the location ofr'the switches connectedto the incoming and outgoing trunks selected for a telephone connection. This signaling system is associated with the marker throughthe incoming primary cross bar switch; the apparatus of the calling incoming trunks. and thence, over circuits established through-the units ofequipment selected for connecting this trunk to the marker. The signaling system isalso connectedjthrough the outgoing secondary cross bar switch; associated with the selected idle outgoing trunk, to the marker over circuits established through units of equipment selected for connectingthis outgoing trunk to the marker.

In this signaling: system electrical currents of difierent' frequencies are variously combined-to ."obtain a large plurality'of difierent signals equivalent to the largev plurality of switch frames in the machine switching ofiice; The 'signalingsystem is also'used for indications to the marker that the trunks of the group tested are all busy and that 'a'group of trunks has been added to this regulargroupof trunks and thatthe added group may be found on a'difierent frame'from the. one on' which the regular trunks are located.

In this case the si'gnalingisystem causes'an adiju'stment of the apparatus in the marker for associating the marker with the added group of If an idle trunk is selected from the paratus is in general as shown in Fig. 8 of Patent 2,236,246 to G. V. King et al. and as shown in Fig. :1 of the accompanying drawings.

.The patent shows one signaltransrnitting set and the accompanying drawings show two such signal transmittingsets I00 andllll, each set comprises a plurality of current sources-which are shown as generators or oscillators, each having an amplifying system and eachhaving associated therewithav plurality of resistances for distributing the load and to facilitate the connection of frequency combinations with. transformers associated with each cross bar switch frame. Eight generators are shown in each set, each generator supplying current of a different frequency, each set is the'same'and, therefore, the current sources .of each set are of. the :same eight frequencies.

The output or three amplifiers is combined for each.multifrequencyssignal.and thus currents of three frequencies are simultaneously. transmitted bar switches on this frame. combinations of three frequencies each, may be ir om the current source 's'et to "the receiving cirthree different frequencies over leads "1'80 and 'I 8l. These rlea'ds are connected to the equipment of-vazparticular cross bar switch frame which comprises transfchmers and the select magnets associated with the horizontal contacts of "the cross A large number of connected to the equipment of the various cross bar switch flames or equipment of the office to supply different signaling current combinations to each one of the frames of the equipment throughout the'ofiice. will be apparent from the circuit drawing the current of three different frequencies connected to lead 181 extends through thecontact of the iirame relay 2B2, primary winding of transformer 22!, returning to the amplifiers over lead 180 to ground in each The currents of different frequencies are transmitted to the secondary coil of transfarmer 221', thence through windings of select magnets such a 212 or M3 on this frame of switches, to the input winding of transformer 403 where a connection is established by the selected trunk and marker equipment. The secondary of transformer 403' is connected to the receiving circuits of the marker. The combination of three frequencies is :thusytransrnitted to the receiving circuit of themarker that is coinpleting a telephone connection and'this signal, as later described, supplies the marker with the location of the switches associated with the trunks is actuated by the current source of a given frequency. As h e-rein stated, three frequencies are simultaneously transmitted by transmitting set I00 or transmitting set H0 and in consequence of this, three receiving. circuits of the marker ar actuated. The frequencies trans mitted energize the tubes in each of the three receiving circuits which create a plate; current for operating three relays, such as relays 421, 422 and 42-3. A group of relays 42!) is selectively operated by therelays associated with each receiving circuit'which make'a combination for associating a signal path with a particular lead resulting from the three frequencies connected to the receiving circuits. This signal is transmitted to-cut-in relays depending upon whether the indication to be transmitted applies to an incoming trunk or an outgoing trunk. If the signal applies to an incoming trunk, the incoming trunk switch cut-in relay 435 is energizedby the marker which then operates the incoming trunk'switch location relay 430 to associate the marker equipment with switches connected to the trunk. Likewise, a similar signal is transmitted from three other frequency sources to again operate the receiv= ing circuits whi'clii'n this" case will operate three different receiving circuits so that a different combination oi relays 420 is. energized. The marker at this time: energizes the outgoing trunk cutinrelay 436 which energizes the outgoing trunk switch location relay, such as 43L to give the marker the. location of the switches connected to the selected outgoingtrunk. 0

The calling incoming trunk may be any trunk located in any group of frames and a path through the cross bar switches must be found to a selected outgoing trunk switch onany of the outgoing frames. Combinations. of incoming secondary and outgoing primary cross bar switches must, therefore, be operated for con necting the talking andsignaling leads between any of the incoming primary crossbar switches and any of the outgoing secondary switches. The marker is thus guided by the multifrequency signaling combinations to associate itself with particular frame connectors such as shown in the aforementionedpatent to King et 3,1: to reach frames having switches to be used for establishifig connections responsive to the registrations recorded in the marker. Connectors of this character are associated with all-flames or the oihce associated withboth the iiico ming and outgoing trunks. In this manner,-the switches of the automatic switching telephone-ofh-ceare energized for connecting an, incoming calling lirife with outgoing trunk or outgoing linei- Asherein stated, two multifreqiiency; current transmitting sets I96 and H0 are used in the automatic switching telephone office in orderthat a failure in one willnot afiect the completion of telephone connections and'the control circuit of the invention is organized to control the transfer from one transmitting set to the other under varied conditions which may be encountered to guard the switching equipment against failures of any character. 'The control circuit of the-invention has relays A-shown in Fig: 2 associated with three frames or-trunk switches, one relay per frame; for connecting the multifrequ'ricy current supply set R30 to the teleprione'switcln ing system and relays B associated with three frames of trunk switches; one relay per name, for connecting the iiiultifrequenc'y ctrrent s'ua ply set no to the telephone switching The'relays'A and B are operated by" the can 'ol circuit automatically responsive to centres in any of various parts" of the multifrdiincy systemas later 'described'in detail. N irially, in order that one multifrequency surrea surely st be used as often as the other,- the stray sets loo-and no are alternately connected with the telephone switching system pens many by the alternate operations of relays A and E'underth'e regulation of switches shown; in i and s. The periodic transformer controll i 'mechanism of Fig'si'?" and s is; however,- automatically made ihefiectiv'e' w enever a failure in the inultiirequencysignaling system occursf Failuresinay occur from a rant man individual marker, inch tirre'qnene circuit, in the equipment associated with a crane fram one the multif'rcuency cirrrent steely lot or he anyof which-bring about the automatic tra sfer to the site-mate current supply set. Should afaiiore occur in the niiiltifreduenoy current suppi'y' set is not at the time in 'us'g the operatioiiof the contfol circuit is are en allya tercaftt, prevent switch ng terms-correc supply st-iiiider any condition until the fault has been reached;

Detail. description The relays A and B, 202 to 201, inclusive, have been shown forthree frames of cross bar switches, frame 0, framei and frame 9 which may be considered as three of the first ten frames in the automatic switching telephone oflice. 'I'he office may have a large number of frames for both incoming and outgoing trunks; Switching equipment has been shown diagrammatically for two frames, frame and frame 9. The multi-' contact relays 200 and 20I each have a number 'of contacts thereon equivalent to the number of three different frequencies from generators or foscillators associated with-amplifiers, the output of each amplifier being connected to as many load distributing or mixer resistances, such as I30, I38, as are required for signal circuits. For convenience these resistances will be known herein as'mixer resistances, one from each of three different amplifiers being connected together to form a combination of currents of three difierent frequencies for a multifrequency signal. An example of the frequenciesof the current output of eight amplifiers, such as may be used in each 'multifrequency current supply sets may be given as'425 cycles, 595 cycles, 76-5 cycles, 935 cycles, 1105 cycles, 1275 cycles, 1445 cycles and 1615 cycles. The oscillators, amplifiers and mixer resistances are furnished in duplicate as shown for sets I00 and I I0, Fig. Lwhich are both constantly energized unless a fault occurs in one of the oscillators or amplifiers. The output of the amplifierv transformers, such astransformer I56, is constantly impressed uponthe mixer resistances and thus a current flow is established whenever any current frequency combination is connected to the mechanism of a marker, such as diagrammatically shown'in Fig. 4 by the selection of a trunk circuit. As shown in the drawings. Figs. 2 and 4, when an outgoing trunk circuit is selected by the marker over lead 232 a relay in trunk 230- responds for connecting ground to lead 23I which operates relay 402 in the marker for connectingrthe combination of curents of three different frequencies with the receiving circuits connected with transformer 403 to establish the location of this trunk for the marker and .the

frame locationof the switches connected to this trunk. The receiving circuits in each marker are tuned to respond to the aforementioned frequencies, one receiving circuit for current of each frequency, Since three frequencies are transmitted simultaneously over a single lead, there are three receiving circuits which respond to operate three corresponding relays in the marker. The combination of relays which is operated for establishingthe switch location is fully described in the aforementioned Patent 2,236,246 to G; V. King et al. and need not be repeated herein. An example is however diagrammatically shown in whichthe energization of receivers Al I, M6 and M! energizesa' relay combination for operating the incoming trunk switch location relay 430 .whenthe cut-in relay 435 is operated and the .energization of receivers 4I0, III and IIB energizes a relay combination for operatingthe outgoing trunk switch location relay I3I when outin relay 436 is operated.

Relay 200 is shown energized which energizes the relays A to connect output current from all amplifiers in the multifrequency current supply set I00 with'the telephone switching system, to be connected in varying combinations to the receiving circuits when an idle trunk is selected by the marker. A failure in some part of the system or the automatic advanceof the'periodic transfer control equipment will disconnect the multifrequency current source supply set I00 from the switching system and connect the multi- ,frequency current source supply set III] to the switching system. a V

The periodic transfer from one multifrequency current source supply set to the other will first be described. The switches shown in Figs. '7 and 8 are arranged to take forty-four steps from the normal position and return thereto for one cycle of operation. By reference to Fig. '7 it will be apparent that when switch brush has traveled step by step over the terminals of switch arc I0! from terminal I to terminal 22 the switch brush I23 will be in position to advance to terminal 23 of switch arc I04 upon the next step forward of the switch brushes. Brush I23 then makes twenty-two forward steps to again arrive in the position shown which also brings brush I20 into the position shown associated with terminal I. Switches I00, 800 and 820 are arranged to operate in this manner. Switches 800 and 820 are continuously operated under the control of interrupters 805 and 825 which, however, may be disconnected by the operation of key 835. Switch I00 is under the control of switch 800.

Each operation of the control circuit is check tested so as to remove the probabilityof failure ability of failure in supplying the multifrequency currents to the marker. A general idea of the periodic transfer equipment will precede the detailed description of this equipment. It will be noted that relays3l2, 3II, 3I3, 3I4 and 3I5 are shown energized in order that one of the multifrequency current supply sets may be shown actively serving the telephone switching system. A circuit is thus established for relay 200 from ground through its winding contact 3 of relay 3| 2, resistance 30! to battery. This position of these relays is checked by the control circuit as later described. Circuits are established'for relays 3| I and 3 I3 by the current supply sets. Each amplifier of the current supply sets has a rectifier connected to the .output coil of its transformer for creating a direct current circuit to operate relays I20, I 2| to I21 in current supply set I 00 and relays I90, I 9| to I92 in current supply set 'I I0, Since all amplifiers are normally energized by their associated oscillators these relays are all normally operated and a chain circuit is thus mechanism. as later, clescribed. The release of any 3l'l5from'b atter'y, 'throu'gliits winding, "conduc tor. 'lqijb u n no of, "switch at; tel; contact-J1 of may WTP ound: I 1? The cdntitolic'ircuit v is s wn arran ed to disconnect one multifre'quency supply set, from the switching systemi'and connect the other one'there to eY eighty-eight stepsiofswitch' one which 8.9? 2 r a nced n n sea e t i W 55 a d 825 n iete f u t i q eh v fd 'a e m n s! 'thr ue s t h magnet $9 1 bat r n e o he m h switch magnet 82!) to battery! The. switches therefore are started forward" for counting ape o of ti w e the m l ifre uen c rr nt s nplyset III?) "is connected totl letele'phone switching equipment! W e b u h 9?! reac es rm na o'er are 80: a circuit is establis c1 forrelay e3 0 from battery, through the-winding of this relay, switch terminal and brush 80 over conductor 840 to ground on key 5 i 9.' Relay 830 in operating establishes a locking circuit for itself through its contact 2, contact of relay 831 to ground .over

conductor 84fl. When switch brush 835 reaches term al 9; ofiarc 82I a circuit is established forrelayl832=frombatterm through its winding, contact and brush,;as recited, :to-ground, over 0011'- duster 3.4.0. It will be noted tha-tztliis relay. op-

erates when brush 835 reachesfiterminal v4 butterthe first operation as now being described the relay will release without producing any.action,- terminal 4 is used upon the next cycle of this switch.-

This relayremains operated during the time that brush 83. is res g on terminal flrvlhich shunts thewinding .of relay, 83Ls0 thatthe latter. relay does not operate until brush 835 moves off of ter- 9- Atthis me a c rcuit isestablished for re lay tg igltfrom battery in seriesywith relay 8,32,

contact of relay 832;, Contact I of relay 830 to ground, over. conductor ME], The operation of relay 33] opens the locking circuit .for relay '830 whi elease s r ea i both re ays 8.32 and 8}]; iii switch vbrush 86.8 arrives at terminal 15 an re ay .8 9 h s not bee prope ly; released by the action of switchfiZil a circuit is established for relay l3 which maybe traced from battery, through the windin of thisrelay, contact 3 of elay 18 rminal. i o later l", 1 1 113 11 grouniiover conductor 1 @459. Thisindi ates that w'its es flaed 26 r 'n ste i g in 11 111- sonata consequently lamp-fil is lightgdfrgum battery q r b s fi ament 9 9t?. 1f..re1a 6131b audible alarm is also given a a awa may. h tm drQmr 1 i 'ea i ml e J ntree 61, s mester 531 c tab i ie a fi a taet 1. o relay 50s. t battift t r' u h t aid. ble a a m meenanism. Thischeckof the movement of two switches continues every few terminals as is apparent from the switch terminal strapping ,as the switch v rotates from terrjninal j t te'minalj lfig atlislie r, re a '5 l w lfi lmay'b ir n, position one of the control sjwifiqhes; statlisheufto relay? 314 from hat t, r l tesrr a e i for relays5I1'and5IIinmll1 p a slow to release. The latter twoi laysin operat ns one; c r uit which, r ent interfiet ece with the circuit action taking place in the periodic" transfer; mech'anisin'if an automatictr-ansfeiffrbm we should be simultaneously'attnipted'by' devices 'of the control circuit. Tl'i release 5H and attilesame timec en s thecircuit fdr relay 5115: Relay'5l5 inimediately release while relays *5 I 1 and 51 I "incmentaril reniam' in their operated positions? The release" tr relay I {opens I tending through the windings of "relays" 3 I4 and e .tact It of relay 3IZ5',1contaot 1"oftrelay 31:4;contaict' 5* of relay ,3 l 3, windingiofi relayif3 I12; contact 'I "of relay3I3; contact 2 of'rela'y 3'I4,:contact2"bfjr= lay.3I5 to ground: I -";R. elays 314 and 3 I 5. now remain released during the second rotation of fsWitchesBfifl'and't82fl:fiThe following tableggives thedifferent' positions taken by vlffllays 31,4 and 315 andtthe consequent op erated andnorn al positions of'relays3lj2iori3l0, during the rotation of switches BBQ and 100. ,The

' tiacefd" from giro st lt-611i; to'ogaiefadvance iis interrupter 805 and when; brush IBI-Ifinoves away from the terminal 1 44, th circuit for relay I8is open but as pre-' viously statedthisrelay is slow to'release and remains-operated while brush 809 connects. ground through terminallpf arc'802, contact l g'of relay 5I8; winding reIaySI'I and winding of relay 5| I in ,multiple,- ope ra't ethe latter two relays a p event i eri rh e'ir mo e c is of the control;c 1 r.cuit asjpreviousl'y described. Relay 5I-3ir1eleases liich immediately releases relay 5]]5,

openin he ircuitlglthrough the switch magnet 'l00fcausi n thisgswitch to advance fromterminal au-t rmi a hW SIQP.

ten 80p. I

. Switch -to=m1 ltifrequencycurrent supply set 110 I II ByLre ferenc toQthe foregoing table it will be seen; that;-relayf 3I4. remains normal and relay 3I5 is operated and that at this time the multifrequency current supply set I00 is disconnected fromgtheswitching system and multifrequency currentsupply set H0 is connected thereto. The

This occurs after the eightycircuitforrelay3l5 may be traced fr0m battery 7 throughjtswinding, conductor I4I, brush I20,

terminal 3 of arc IN, to ground on contact 4 of normal, thecircuitfor relay 3I2 is opened and a circuit is: established for relay 3I0. The circuit for relay 3 I 0imaywbe traced from battery through resistance 3I-.'I.,'contact 3 of relay 3I5 operated,

contact 3. of; relay 3.I4 normal, contact 5 of relay 3I I, windingwof. relay 3I0, contact I of relay 3| I,

contact 4 ofirelay3I4 normal, contact 4 of relay 3I'5operated to ground. "It may be seen that the circuitfor relay 3I2 is. open by the operation of relay 3I5twhen relayfl3l 4 remains normal since the circuit for this relay is open through contacts land-2 of relay 3I4 orrcontacts I and 2 of relay 3 I 51Whichever viewpointis taken.

:.The' release of relay 3I2 opens the energizing cilicuit'for relay 200 and, therefore, the A relays on all of the switch-frames throughout the auto-- matic switching system are released which dis connect the frequency current supply set I00 from the switching equipment of the oflice. The oper-' ation of relay 3 I 0 establishes an energizing circuit for relay 20I from battery through resistance 306, contact 3 of relay 3I0, winding of relay 20I to ground. Relay 20I establishes obvious circuits framef'i extend through the contacts of B relay which again energizes relay 5I5 causing the energi'zation of switch magnet I00. The switch 800 then steps from'po'sition 44 to position I as previously described, causing the release of relays 5I8 and 5I5, and the deenergization of magnet [00 whichcauses the switch brushes I20 to I25 inclusive,to step from terminal 3 to terminal 4which now brings about the operation of relay 3I4 and therelease of relay 3I5. Relay 3I4 is energized from battery through its winding over conductor v I42; brush I22, terminal4 of arc I03, contact 4 of'relay' I, to ground on key 520. In position 4 I of switch 100, the circuit for relay 3I5 is opened sinceby tracing this circuit over leads 'I4I to brush I20, and terminal 4 of arc 'IOI, it will be found that this circuit extends to contact 4 of relay 5I4 which is normal and at this time open. With relay 3| 4 energized and relay 3I5 normal,

the circuit for relay 3I0 remains energized so that at thistime nochange is made in multiple frequency current supply sets. Switch to multifrequency current-supply set 100 At the end of the next cycle of switch 800 when brush 8I.I reaches terminal 44, relays 5! and 5I5 are again energized to energize magnet 100 which isdeenergized when brush 8 II moves away from terminal 44 causing the brushes of switch I00 to move from terminal 4 to terminal 5. At this time both'relays 3I4 and 3I5 are again energized; relay .3I5 from battery through its winding over conductor 'I4I, .brush'l20, terminal 5 of arc IOI .to ground on contact 4 to relay 5 I4 and relay 3 I4 from battery through its winding, conductor 'I42, brush I22 and terminal 5 of arc I03, contact 4 of relay 50I to ground on key 520. The operationv of both relays 3I4 and 3I5 after'the second eighty-eight steps of switch 800, deenergizes relay 3I0 and energizes relay 3 I2 for transferring from current frequency supply set IIO back to current for the B relays on each frame of the automatic Y switching ofiice, three of which are indicated 203,

205' and 201. The amplifiers of supply setv IIO thereof which are shown, furnish current of the? same frequencies and in the same order as the amplifiers shown forset I00 and, therefore, the

the contacts of the A 'or B relays to the switching I equipment of the oilice which are all transferred at -the sameftime. In the present disclosure; con

du'ct'ors'f I80 I8 I from current supply set I00 arffdisconnected by the' release of" the A relay 202*Fand confd'uctors" I82 and I83 from current:

supplysetfllo are now connected through-the contacts joffthe B relay203 to transformer 22I'.v Theleads'shown connected to transformer 223,

frequency-supply set I00. The circuit-which is opened for relay-3I0 and the circuit-which is established-for relay 3I2 are believed clear'and need not be'repeated. The release of relay 3I0' .opens the circuit of relay 20I which releases the B relays'on all frames of the omce to disconnect' the amplifiers of the multiple frequency current simply set H0. The operation of relay 200 through contact 3 of relay 3 I2 operates the A relays on all of the frames throughout the switching system to connect the amplifiers of multiple stepping of switch I00 under the control of switch 800 automatically causes the connection of. alter-' nate multifrequency current supply sets to the mechanism of the automatic telephone switching, system-every eighty-eight steps of switch 800,l1i 1 Let it now'be assumed that a failure' o'ccurs; in one of th'amplifiers'or one of the oscillators Linj mui-tifrequency current supply set I00 which at'this'tim'e is connected to the automaticswitch Y Multiffeouencygcurrent supply s et failure ing telephone system. This .Would mean. that relay 31.4 and relay 315 are either lboth operated the periodic switching arrangement controlled.

y t e w ches of Fi s. 7 and thin ope ation whi h ha at; t .time .conn ed -the m lt frequency current supply set 100 to the switching I For this description, it will be assumed that there is a fault in the oscillator 1'10 or that tube 160 or 161 has burnedout, either of which would prevent the transmission of current of the frequency generated by oscillator 110 from reachf-theput ettran i m r 5 d the re of this frequency would not be transmitted to the switching system. It would also prevent system.

current from reaching the rectifier 151 and,-

therefore, no current would ilow through the winding of relay 120 and this relay would be, released. Therelease of relay 120 lights lamp 139 and opens the circuit for relay 313, since relay 313 depends for it operating circuit upon all relays being operated which are associated with all jof the amplifiers in the niultifrequency current supply set 100. "The release of relay 313 opens'theenergizing circuit for relay 312 and the release of relay 312 opens the energizing cir-i cuit for 'r'ela'y 200 which releases the A relays on allframes in the'oflice, three of which are shown, 202,204 arid 20B, Therelease of the latter relays opens the multifrequen'cy current, supply to the frame transformers such as 221 and 223,and,;consequently, opens the multifre quency current supply set to the receiving circuits of the marker. Th releas of" relay 313 establishes acircuit for elay 611 which may be traced froin'battery through the Winding of the,latter 1'e1a'y',contact3 of relay 313, conductor 3'40whichext'ends to ground on release key 515. Relay 002 is operated from battery through its left winding, contact" 1"of relay 511, contact 2 of relay 313, contact '2 of relay 31 4, contact'2 of relay 3'15 to ground. It will be remembered that atthi's time relays 314 and 315 may either be'both operated or both released. Relay 602 in operating establishes a circuit for relay 514 traced from battery through its winding, contact 2 of relay 002 contact '3 of relay 512 to ground. The operationbf relay 514 either operates or releases relay 31'5 dependin g'upon the position of the latter relay at this time. The circuit for relay 315 may' be traced frombattery through its windingjthence overcondu-ctor '141,'-.brush E20 or'123"througha terminal of are 101 or 104 which mayb p'en' or conne'cted to ground on relay 514 dependingu'pon the position of brush 1'20 or brush 123 at this time. It is apparent that if brush 120 or brush '1 23 is resting on an odd numbered terminal, a circuit to ground is established with'rela-y 514 released. Under this circumstance, relay 315 at this time will be operated and th'e operation of relay5 14 would release relay 315. If brush '120-orbrush 123 at this time is connected with'an'even numbered terminalof arc'lfll or l04 with relay '514- released, no circuit would have beenestablished for relay ..315--and underkthis circumstance it contact and armature 4 of relay 314 energized,

contact 1' of relay 311, winding of relay 310, contact 5 of relay 311, innercontact and armature 3 of relay 314 energized, contact 3 of relay 31:5 released, resistance 311 to battery. A circuit is now established for multicontact relay 201 from battery through resistance306, contact 3 of relay 310,winding of relay 201 to ground- All of the i8 .framerelays throughout the switching, system such asrelays 203, 205 and 20'1-are now energized for connecting the leads from all of the amplifiers in multifrequency current supply set 110 to the transformers such :as 221 and 223 associated-with the switches of the telephone office. Referring back to the operation of relay 511 which was operated. by the release of relay 313, this relay in operating establishes a locking circuit for itself through-its contact 4 to ground on key519. Lamp 51.6 is lighted .to give a visual signal indicating a failure and a circuit is established for relay 612 from battery through its light winding, contact2 of. relay 011 to ground. An, audible alarm is sounded by the operation of; relay 1 512; which completes acircuit for alarm 535 extending from battery through this, alarm equipment contact 1 of ,relay 503, contact 1,-of relay .504 ,'conductor 531 to ground on contact 2 of relay 612. The operation of relay-512 holds 're1ay515 operated ifit was from operating if it was. not operated. 'Thissis done toprevent an automatic transfer from one multifrequency current supply'setto the other mature and outer contact to a point between the relay winding and resistance 5lBwhich holds relay 515 shunted'so that this relay cannot be operated byaground throughcontact 2 of relay 5 18 -if,relay;518 is operated by switch 800 after the shunt connection is made. If relay 518 should-at this time be operatedby the switching equipment ;of Figs. "'land 8, the switch 1001s not moved and .the automatic wtransfer will not again be'in possession of the controlcircuit until the fault has been corrected in the amplifier circuit. Key 521 maybe operated whichenergizes relay-5H over an obvious circuit. Relay 512 holds the *ground' Lshuntxon relay 515 or the operating ground on'relay 515 through its contact 3. Relay :512 also. establishes. a locking circuit for relay 514gwhich, as will be remembered, was operatedby relay-1502i L When the correction in the amplifier has been made, restoring the currentoutput tothe transformi' I56 of the-amplifier; relay is again operated which reestablishes the circuit for relay 3L3. With the control circuit equipment in the positions asherein described, the operation of relay 3| 3 will not at thistime function to change" B the position of any of the'equipment. The operation' of-relay 120 extinguisheslamp' |39. The attendantwho has'repaired the amplifier equipment'how 'operatesthe" release key |9. The

operation of this key releases relaysfillz, BIZ and :10:

the periodic transfer 'is" now restored. Normally,

at this time if relay 315 has been operated because of the 'failure'it would be released and if released becauseo f the failure it would be reoperated. Consequently, themultifrequency supply'setlin useat the time that the failure occurred would be restoredto'use. This, however,

might be autorriatic'ally changed a short period thereafter by th 'perioldictran s'fer equipm nt controlled by th'e switches or; Figs. 7 and 8.

of relay 3|3 establishes a circuit for relay 6H from battery through its winding, contact 3 of relay 3|3', conductor '340'toground on a contact of key 5| 9.: The release of relay 3| I would establ'ishalcircuit 'forreIay GIO from battery through its winding, contact 310i relay 3| I, conductor 340 to ground'on a contact of relay 5|9. The operation of relay 6| lllights lam'p 6|6 as a'visual indication that multifrequency current supply set I00 has 'a fault therein 'and the operation of relay 6|0 liglits lamp MS as a visual indication that multifrequency current supply set I ID has a fault therein. 'I'h'eoperation of either of these relays establishes a'circuit from'ground'over conductor 53?, contact ofrelay-EEM, contact of relay 503, audible alarm circuit 535 to battery giving an audible'alarm so that the fault inthe multifrerquency supply set which is not .serving an oflice will be immediately repai'red i Since themultifrequencycurrent supply set in which the failure cccurred was not connected to the switching system, no interruption results from the failure and, consequently, the mechanism for transferring the switching system to the Intheforegoingdescription 'a failure in multi- '25 other supply set is not-operated-under this confrequency current supply set |0|l was described and the same description may apply to a failure inthe'frhultifrequency current supply set H0, with the exception that'this would cause the redition. In this case, no circuit is established for the operationoilrelayEiM which as previously outlined is the first relay to. be operated in the mechanism -for making a transfer from one multilease of relay 3| instead of the release of relay [80' frequency current supply set to the other. The

M3. The released relay-3H causes the operation in relay BIO insteadof relay 6|| previously described when relay 3| 3 was released. If at this timetlie multifrequency'current' supply set |||l circuit for relay- 2, aspreviously explained, was established through its left winding, contact of relay 5| I, contact ofthe released relay depending upon whether itwas. 3|| or. 3|3, thence was connected to the ofiiceswitchingsystem, re- 135 through the contacts of relays" 3|4 and 3|5 to lays 3M and Elli pare formed into a difierent combination than would bethe formationifmultifrequency {current supply circuit |00 had been connected to jth ofilce switching system. By reference to the chart'herein given it will be noted i that when-the in'ultifreqiiency current supply set ground. However, by reference to the chart, it will be apparent that if multifrequency current supply set I00 is connected to the office, relays 3| 3 and (2 are energized and the circuit for relay 3| 2 canfonly beestablished with relays 3|4 and 3|5 both'o'perated orboth released. Under this |U"' is:c6nnected to the ofllce switching system,----circurnstance, if relay 3|| should release, a cirrelay 3| Q isjoperateld "and relay '3 2' is f released or whichcirc'iiit is' 'establi'shed-"by'the combination formed of relays 3|;4 and '3|5."Inone case relay 3|5 is operatedand relay 3M isreleased' and in the other ease -relay 3|4i's operated and relay 3 I5 is released. Consequently, relay 6|0 establishes Since the oscillators for "sou 'inultifrequency current supply-sets are in continuous operation and consequently the-current is constantlytransmitted from 'all of the output transformers of the amplifiers vwhet-her these'amplifiers are connected to the 'swit-chin'gtmechanism oifice or not, a failurem'ay 'occuriin an amplifier of the 'multifre-' quency current" supply set which is not at the time'co'nn'ected to the switching system of the, office; The life ofan amplifier tube having been exhausted wouldautomatically cause a release .cuit could not be established for. relay 602 since theci'r cuit for. this relay is not established to ground through contacts 4 of relays,3|4 and 315 since one of .the contacts for establishing this circuitis open. I V V V The foregoing Would'also be true if the multifrequency currentfsupply set H0 is connected to o the ofiice and a failure occurred in current supply set I00; This'would be the case when relay 3 and relay 3|0'are both operated. The circuitfor relay.3|0 is onlye'stabli'shed when one of relays 3M and CH5 isreleased andthe other one operated. If relay3|3 were released at this time because of a failure in the multifrequency current supply set 100. notconnected-to the switching system, no circuit will be established for relay 60% because the circuit forthis why would extend through contact Z -of relay 3 I73 released but since one of rel-aysil -fl and 3|5 is operated and the other releasedQno circuit to ground would be established through contacts 2 of the latter relays.- During-the-time that a'repair is being made in the multifrequency current supply set which is not in-use, key 52| is operated which operates relay 5|2 to connect ground with the winding of relay 5|5 to either maintain this relay operated of a relay'isuch'jas I20,:or: I90 and consequently 7 ifit is at this time operated -or to place a shunt OPIIfthE circuitfor: relay 3||or relay 3|3 depending upon the .current'supplyset not in use. The amplifier relay which was releasedestablishes a circuit'for its associated lamprto indicate the around its winding to prevent itsoperation by *relay 5|8,as previously explained.- Thisprevents the switches of Figs. '7 and 8' from automatically transferring the switching system to the multiamplifierwhich hada fault therein. The release 75 frequency current supply set under repair,

armo

ai re, n marker Relay 442 is included in each marker and is operatedif the marker fails to obtain a satisfactory multifrequency switch location signal. Conductor 441 extends to all mechanism in the marker which could cause such a failure and in case of failure associates a ground with conductor 441 for operating relay 442. Relay 442 connects ground with conductor 443 which extends through contact 2 of relay 551, winding of relay 603 to battery. Relay 603 in operating estab-' lishes a locking circuit for itselfover lead 340 to ground on releasekey. 519. A oircuit for lighting lamp 601 is established through contact 3 of relay 603 .to indicate to an attendant that trouble has occurred in an individual marker which has not received a satisfactory multifrequency current signal. A circuit for relay 514 is established by relay 603 which may be traced from battery through the winding of relay 514, contact 1 of relay 612, contact 4 of relay 512, contact 1 of relay 603 to a ground on the contact of relay 600 or 601 whichever relay is operated depending upon the multifrequency current supply set in use at the time. The circuit for either relay 600 or 601 is also established through the contacts of relay 603, the circuit for relay 600 may be traced from battery through its winding, contact 1 of relay 1501, contact 2 of relay 310, if 310 is operated, contact 5 of relay 1503, contact 1 of relay 1502, contact 3 of relay 511 to ground on the release key 519. A circuit traced for relay 600- is only established when relay 310 is energized and therefore is only established when the multifrequency current supply set 110 is connected with the switching system. If multifrequency current supply set 100 is associated with the switching system when this character of failure occurs, a circuit is established for relay 601 from battery through its winding, contact 1 of relay 600 which would then be normal, contact 2 of relay 3,12 operated, contact 5 of relay 603, contact 1 of relay B02, contact 3 of relay 511 and thence to ground on key 519. Relay 603 also establishes a circuit for an audible alarm by connecting ground through its contact 2 to conductor 53'1, contact 1 of relay 5 04, contact 1 of relay 503 through the audible alarm equipment 535 to battery.

The operation of relay 514 connects ground through its contact 1 to the armature f relay 515 which holds relay 515 operated, if it was already operated or prevents it from being operated by placing a shunt around'resistance 516 and the winding of this relay. As herein stated this action prevents automatic switching of the multifrequency. supply sets .by the switches in Figs. '7 and 8 if at the time the switches have arrived in position to operate relay 510 or do so shortly after a failure occurs. In either case switch 100 i preventfid, rom advancing to the next terminal. The positions of relays 314 and 315 is now altered for switching from one multifrequency supply set to another. Let it be assumed that relay 315 is released and that relay 314 is energized before relay 514is operated. By operating relay 514 a circuit is established for energizing relay 315 from battery through its winding, conductor 141, brush 120 or 123; any even numbered terminal of switch are 101, or 123. to groundon contact 4 of relay 514. It w ll be seen that if brush 120 or 123 were restingon an o d n b re te minal. re ay 3.15 would a r a y.

av b en perated. to round on contact 4of that relay 314 was normal and relay 315 normal" is to change the formation of relays 315 and 314 so that the alternate multifrequency current supply set is taken for use. As for this example, I

relay 315 is operated in response to the operation of relay 514 and consequently if relay 314jshould have been in an operated or released condition: the formation would be changed so that under one condition a switch would be made fromsupply set to supply set 1 10 and undr t hlf condition a switch would be made from supply: set to supply set 100. Let it nOW, he assumed before the, operation of relay 514. Under condition relay 312 is energized for connecting multifrequency supply set 100 to. the switching system. By operating relay 31,5 responsive to, the operation of relay 514 and leaving relay 314 normal, relay 312 is automatically, released and.

a circuit is established for relay 310 throughcon tacts 4 of relays 314 and 315 so that the transfer made from m l frequenoy current s p ly-s 100 to multifrequency current supply set 7110, Under this condition relays 31.1 and. 313 are not involved in the transfer as was thecase when, a

failure occurred in an amplifier or osci llatorinv An a 1 v sounded, ndic t n lamps ar lighted. and, a an fmul i re ueno o r cm. p y se is effected when frame relay 1 1. as, r l y 4 a l d t ra e. hiswouldo so ar effect if all A relays o all 3 relays. fail to.

operate when a transfer of multifrequency cure ppl sets s, t mpted b tv not ompleted. because of, a fault in acontrol circuit relay as relays 310, 3.12, 314 or 315.. First, let it be. assumed that relay 20 4failed to operatein resp onse to the operation of relay 2 00 forconnect ins, the multifrequen y su ply set 00. tot It wil ans r s o d. th eac ramebe no ed. t ay 3 .0. is. anormall o erated. rela w t relays -A o er tedand re ays B re= through resistance 209 to battery. If relay'204, as assum d. fa d to peratehe circuit for elay 300, is opene ausin it to. rel ase which causesa series of rapid operationsin the cone trol circuit. The frame relays 202 to. 201 are wired in groups often frames and a, relay such,

as 300 is. provided for eachten frames. of switch. ing equipment. The circuit. for relay 300 extends through they frame relays of ten frames, three frames being shown. One relay such as 301 is also. provided for, each ten frames. Ten relays, such as. 321, 3.22 and 323, are provided, forall of the frames of. the office. The probability is as-. sumed that failure would occur in only one frame relay atone time so, that. they ten relays I and ten lamps shown in thelowerportion of Fig. 3' will be sufiicient for the entire. office to. designate one of the relays which failed to oper a in ny of t e fr e group The, release of relay 3.00, establishes an gizing circuit for.relay 30.1' from. batter 211? hi its winding. contact 2 of relay 300, contact :I of relay 5, contact [of relay 602, contact 3 of relay 5 to ground on key 5I9. Relay 300 also establishes a circuitfromground through its contact I, resistance 5l9 and the non-linear resistance 5I0 winding of relay 504 to battery. This ground must be associated with thermistor 510 for a period of timevinv order to cause a current of suflicient strength to fiow through it to operate relay 504. At this time relay 504 is energized to light lamp 501 and sound a major alarm by associating groundthrough its contact 4 with alarm equipment 542. Relay MI in operating connects ground through its contact I filament of lamp 302 to battery lighting lamp 302 and ground through its contact G filament of lamp 303 to battery lighting lamp 303. There are a plurality of lamps of this character connected with a plurality of relays such as 30I and the, lamps are arranged in order on a signal indicating'board. When lamp 302 is lighted it indicatesthe particular ten framesin which a failure occurred and the lighting of lamp 303 indicates the type of switching frames, that is, whether the frame is an incoming trunk switching frame, an outgoing trunk switching frame or another type of frame associated with toll equipment 7 By the lighting of lamps 302 and 303 it is therefore known that the failure of the frame relay occurred in a particular group "of ten frames which are in a particular line-up of frames. The lighting of a lamp 324, 325 or 326 will now indicate that the failure occurred in frame 0, frame 5 orframe l0 in this particular block often frames represented by lamp 302. Relay 320 connects the ten relays which are herein represented by. only three relays 32l, 322 and 323.with the frame relays, one of which has failed to operate. Assuming that the relay which failed to operate is frame relay 204, a circuit is established for relay 322 from ground through contact .4 of relay 204 released, contact 4 of relay 205 released, contact 2 of relay 320, winding of relay 322 to battery. The remaining relays, such as 32l and 323, would nothavea circuit established because the associated A relays 202 and 206 are at this time operated. Relay 322 in operating establishes a locking circuit for itself which may be traced through its contact I over conductor 33l, contact I of relay 512 to ground'on contact 3 of relay 50l when this relay is operatedas will be explained in the followingparagraph. .Relay322 in operating also lights lamp325 overan obvious circuit to indicate the particular frame having a relay therein which has failed to operate. 7

Relay 301 which operated upon the release of relay 300 establishes a. circuit for relay 6|2 which may be traced fromground on contact 4 of relay 30| through the right winding of relay M2 to battery. Relay 612 in operating establishes a circuit from ground on its contact 3 over conductor 531 to actuatejalarm 535 'as previously traced. Relay 30l establishes arcircuit for relay 60001 60! depending upon whether the failure occurred in the A relays or the B relays which also depends upon which multifrequency. current supply set was .at the time associated with the switching system. Since we haveassumed that the failure occurred in relay 204 a circuit is established for' relay' 60l from battery through its winding, contact. l of relay 600, contact 2.of relay'3l2 ope'ratedgcontact 2of relay 30], contact I of relay ,5I5,.contact'|. of relay 602, contact 3 of relay. 5H .to ground on key 5 l 9. This is the locked. Relay 60 l' in 2 operating establishes an obvious circuit for lamp 605 to'indicate the multifrequency current supply set which is atthe time serving .the switching system. A circuit'is establishedfor relay'502 which may be traced from battery through its winding, contact I of relay 5I2, conductor 33I, contact I of relay322, contact 2 of relay 320; contact 4 of relay 205 released to ground oncontact 4 of relay 204 re- 10 leasedq Relay '50l energizes-and relay 502 is locked over acircuit which may be traced from battery through the winding of relay 50l, right winding of'relay 502, contacts I and 2 of relay .502, contact I of relay 5l 5, 'contact l of relay; 602, contact 3 ofrelay 5| l to ground on key 5|9.

As previously stated, theoperation of relay 50l closes a locking circuit for relay 322 to retain if at this time it is operated or by operating same ground to whic'h'relay30l is at this time relay3l4 if at thistimeit is released. Since relay 204 associated with multifrequency supply set I00-was assumed as the relay which failed, the transfer will be made from multifrequency current supply set I00 to multifrequency current supply set 0. For this purpose itwill be assumed that both'relays-3l5 and 3l4 are in an operated position and that the operation of relay 50I-causes the release of relay 3I4.- This would assume that switch brushl22 or is associated at the time the terminal I, 4, 5 or similarly strap terminal inarc 103 or -106 which establishes a circuit for operating relay v3M through contact 4 of relay 50l to ground'on key 520. The operation of relay 50! will open this circuit and release relay 3l4. Relay3|5 therefore is now operated and relay 3l4 released which opens the circuit for relay M2 and establishes the-circuit for relay 3l0 as previously traced for this combination of these relays. 1 I I r I The operation of relay 50 l-also opens the circuit for relay 320 which-releases. -This, however,-

does not interfere with the lamp signals giving the location of therelay since the relays lighting these lamps are locked in position. The attendant upon observingthe trouble by the illumination of the aforementioned lamps operates key 52I which operates relay 5l2 to associate ground with the winding of relay 5I5 which as herein described prevents interference from the periodic transfer mechanism ofFigs. '7 and 8.

When the trouble'ha's been repaired this attendant restores key 52l and operates key 519 which releases relays 502, 50!, [H2 and 30! and the units relay 322 and the circuit is restored to the position and condition before the fault occurred. The restoring of the control circuit as previously explained, is automatically controlled by the periodic switching equipment of Figs. 7 and8 and the control relays associated therewith.

. It was brought out in the foregoing description thatone relay 300 and one relay 30l are connected to each of a plurality of groups of A and B frame relays, each, group comprising ten vA relays and ten B relays for each group of ten frames in the automatic switching ofiice. Let it now be assumed that multi-frequency current supply set H0 is connected to the switching equipment of the office with all B relays operated from multifrequency current supply set H0 to multifrequency current. supply set I- Let. it also beassumed that. a failure occurred in the control mechanism which prevented the operation of relay 3I2- when circuits were established for this transfer. Because of the attempted transfer of current supply sets, relay 3H1 would have been released and, therefore, if relay 3!! did not operate circuits would not be established for either relay=200 or relay l. Under this condition both the A- relays on all frames in the office and the B relays on all frames in the office are released. Relay 300 connected with all frame groups is thus released and relay 30| associated with all frame groups is operated to light their individual lamps which indicate-that the failure effects the entireswitching system. Relay 320 is thus operated and theten units relays Hi to 323 are operated to light the ten lamps connected with those relayswhich indicates that all A and B relays of a group are released. It is clear from the foregoing description and the drawings that the operation of" the relay 301 immediately causes the multifrequency current supply set llll to be reconnected to the switching system of this oflice by the reoperation of the B relays. The leads through the contacts of all relays 300 and 3M extending to the mechanism of the control circuit are strapped together so that each or all of these relays effects the same operations in the control circuit. An attendant observing the lamp signals may easily analyze this trouble. The multifrequency current supply set H0 now remains connected to the oflice switching system until the fault has been corrected.

What is claimed is:

1. In an automatic switching telephone office, trunks, switches mounted on a plurality of frames forming a switching system for completing telephone connections, markers for operating said switches, selectively operable switch locating devices in said markers, a multifrequency signaling system comprising duplicate multifrequency current supply sets common to the switches of said office, each set having a plurality of current sources of different frequencies, a plurality of receiving circuits in each marker tuned to the different frequencies of the current sources in said duplicate multifrequency current supply sets, selectively actuated by currents connected thereto from one of said supply sets, a control mechanism, means in said control mechanism for connecting one of said multifrequency current supply sets to said switching system, means in said marker responsive to the selection of trunks connected to switches for connecting current sources from said current supply set to the receiving circuits of said marker for operating switch locating devices to direct the marker in the operation of the switches connected with said trunks for completing a telephone connection, a periodically operating device in said control mechanism, and means automatically responsive to the operation of said device for periodically disconnecting one multifrequency current supply set from said switching system and for connecting the alternate one of said duplicate multifrequency current supply sets there- 2. In an automatic switching telephone ofiice,

trunks, switches mounted on a plurality of frames forming a switching system for completing telephone connections, markers for operating said switches, selectively operable'switch locating devices in said markers, a multifrequencysignaling system comprising duplicate multifrequency cur-- rentsupplv sets common; to the. switches of: said Qfiice, each. set haying a plurality' of current.

sources of: different-frequencies, a plurality of receiving circuits in. each marker tuned to the different frequenciesof the current sources in said duplicate-multifrequency current supply sets, selectively actuated bycurrents connected there to: from one of said supply sets, a control mechanism, means in said control mechanism for corn. necting one of said multifrequency currentsupply sets to said switching system, means in said marker responsive to the selection 'of trunksconnected to switches for connecting current sources from said current supply set to the receiving circuits of said marker for operating switch locating devices to direct the marker in the operation of the switches connected with said'trunks for completing a telephone connection, and means'automatically operable in said control mechanism responsive to a failure in said multifrequency-sige naling system for disconnecting the one multifrequency current supply set from said switching system and for connecting the alternate oneof said duplicate multifrequency current supply-sets thereto.

3. In an automatic switching telephone ofiice, trunks, switches mounted on a plurality of frames forming a switching system for completing telephone connections, markers for operating said switches, selectively operable switch locating devices in said markers, a multifrequency signalingsystem comprising duplicate multifrequency current supply sets common to the switches of'said ofilce, each set having a plurality of current sources of different frequencies, a plurality 'of receiving circuits in each marker tuned to the different frequencies of the current sources in said duplicate current supply sets, selectively-actuated by currents connected thereto from one of said multifrequency supply sets, a control mechanism, means in said control mechanism for connecting one of said multifrequency current supply sets to said switching system, means in said marker responsive to the selection or trunks connected to switches for connecting current sources from said multifrequency current supply: set to the receiving circuits of said marker for operating switch locating devices to direct the marker in the operation of switches connected with said trunks for completing a telephone; connection, automatically operable periodic transfer mechanism for periodically disconnecting: onemultifrequency current supply set from said switching system and for connecting the alternate one of said duplicate multifrequency'current supply sets thereto and means, automate ically operable in said control mechanism responsive to a failure in the multifrequeneyssupply set connected to said switching system for nullifying said periodic transfer control. mecha-. nism, for disconnecting the multifrequency sup.- ply set which failed and for connecting the, alternate one of said duplicate multifrequency current supply sets to'said switching system.

4.'In an automatic switching telephone office, trunks, switches mounted on a plurality of frames forming a switching system for completing telephone connections, markers for operating said switches, selectively operable switch locating devices in said marker-s, a multifrequencysignaling system comprising duplicate multifrequency current supply sets common'to the switches of, said oflice, each set havinga plurality of. current sources of different frequenciesa plurality: of receiving circuits. each marker, tuned to the difge ferent frequencies of the current sources in said duplicate multifrequency current supply sets, selectively actuated bycurrents connected thereto from one of said supply sets, acontrol mechanism, means in said control mechanism for connecting one of said multifrequency current supply sets to .said switching system, means in said marker responsive to the selection of trunks connected to switches for connecting current sources from said current supply set to the receiving circuits of said marker for operating switch locating devices to direct the marker in the operation of switches connected with said trunks for completing a telephone connection and means automatically operable in said marker responsive to the failure of said marker to receive a multifrequency switch locating signal for actuating said control mechanism to disconnect said one multifrequency current supply set from said switching system and for connecting the alternate one of said duplicate multifrequency current supply sets thereto.

5. In an automatic switching telephone oilice, trunks, switches mounted on a plurality of frames forming a switching system for completing telephone connections, markers for operating said switches, selectively operable switch locating devices in said markers, a multifrequency signaling system comprising duplicate multifrequency current supply sets common to the switches of said office, eachset having a plurality of current sources of different frequencies, a plurality of receiving circuits in each marker tuned to the different frequencies of the current sources in said duplicate multifrequency current supply sets, selectively actuated by currents connected thereto from one of said supply sets, a control mechanism, means in said control mechanism for connecting one of said multifrequency current supply sets to said switching system, means in said marker responsive to the selection of trunks connected to switches for connecting current sources from said multifrequency current supply set to the receiving circuits of said marker for operating switch locating devices to direct the marker in the operation of switches connected with said trunks for completing a telephone connection, automatically operable periodic transfer mechanism for periodically disconnecting the one multifrequency current supply set from said switchingsystem and for connecting the alternate one of said duplicate multifrequency current supply sets thereto, means automaticallyv operable in said control mechanism responsive to a failure in the multifrequency supply set connected to said switching system for nullifying said periodic transfer control mechanism, for disconnecting the multifrequency supply set which failed and for connecting the alternate one of said duplicate multifrequency current supply sets to said switching system and means for resettingsaid control'mechanism to reestablish the control of said periodic transfer mechanism.

6. In an automatic switching telephone oiiice, trunks, switches mounted on a plurality of frames forming a switching system for completing telephone connections, markers for operating said switches, selectively operable switch locating devices in said markers, a multifrequency signaling system comprising duplicate multifrequency current supply sets common to the switches of said ofiice, each set having-a plurality of current sources of different frequencies, a plurality of receiving circuits in each marker tuned to the different frequencies of the current sourcesin said duplicate multifrequency current supply sets, selectively actuated by currents connected thereto from one of said supply sets, a control mechanism, means in said control mechanism for connecting one of said multifrequency current supply sets to said switching system, means in said marker responsive to the selection oftrunks connected to switches for connecting current sources from said multifrequency current supply set to the receiving circuits of said marker for operating switch locating devices to direct the.

marker in the operation of switches connected with said trunks for completing a telephone connection, automatically operable periodic transfer mechanism for periodically disconnecting one multifrequency current supply set from said switching system and for connecting the alternate one of said duplicate multifrequency current supply sets thereto and means automatically operable in said control mechanism responsive to a failure in the multifrequency supply set not connected to said switching system for nullifying said periodic transfer mechanism.

7. In an automatic switching telephone office, trunks, switches mounted on a plurality of frames forming a switching system for completing telephone connections, markers for operating said switches, selectively operable switch locating devices in said markers, a multifrequency signaling system comprising duplicate multifrequency current supply sets common to the switches of said oifices each set having a plurality of current sources of different frequencies, a plurality of receiving circuits in each marker tuned to the different frequencies of the current sources in said duplicate multifrequency current supply sets selectively actuated by currents connected thereto from one of said supply sets, a control mecha-- nism, a relay A on each frame of said oflice for connecting certain current sources from one of said duplicate multifrequency current supply sets through the switching mechanism of respective frames to marker receiving circuits, a relay B on each frame of said office for connecting duplicate current sources of the same frequency from the other multifrequency supply set through the same respective switching mechanism to marker receiving circuits, means in said control mechanism for operating relays A on all said frames or relays B on all said frames for connecting one of said multifrequency current supply sets to the switching system of the office, means in said marker responsive to the selection of trunks for connecting current sources from the multifrequency current supply set to the switching system and to the receiving circuits of said marker for operating switch locating devices to direct themarker in the operation of said switches and means in said control mechanism automatically operable for periodically operating alternate relays A and relays B for periodically connecting alternate multifrequency current supply sets to said switching system.

8. In an automatic switching telephone office, trunks, switches mounted on a plurality of frames forming a switching system for completing telephone connections, markers for operating said switches, selectively operable switch locating devices in said markers, a multifrequency signaling system comprising duplicate multifrequency current supply sets common to the switches of said oflice, each set having a plurality of current sources of different frequencies, a plurality of receiving circuits in each marker tuned to the dif-: ferent frequencies of the current'sources in said 

